British colonisers turned Pacific islanders into some of the fattest people in the world by trying civilise them with fried food, a study by Oxford University has found.

Islanders on Nauru and the Cook Islands in the Pacific have the highest levels of obesity in the world.

Their average weight gain is increasing at four times the global average, 4.4lbs per decade (2kg) compared with global average of 1.1lbs (0.5kg).

Now researchers at Oxford believe they are discovered the source of their obesity. They suggest that social changes, introduced when the islands were under colonial rule, have significantly contributed to unhealthy diets.

Anthropologists Dr Amy McLennan and Professor Stanley Ulijaszek found that islanders lost many of their traditional food cultivation, preparation and preserving skills after settlers insisted that they learn western ways of eating.

They taught the locals to fry fish rather than eat it raw, and forced them to import unhealthy produce after co-opting farmland for mining.

“Under colonial rule, much changed in how food was sourced, grown and prepared and the social change was swift,” said lead author Dr McLennan

“What happened to the land also changed as colonial agriculture and mining industries expanded. There was an increase in family size meaning food was increasingly imported.”

The tiny island of Nauru

The Cook Islands were taken as a British protectorate in 1888, and became New Zealand's first South Pacific Island colony in 1901 until political independence in 1965.

Meanwhile, the tiny Pacific island of Nauru is a former German and British colony whose Administration was led by Australia until 1968.

Researchers found colonial letters describing how the settlers taught ‘proper’ food habits as part of their attempt to ‘civilise’ the islanders

Colonial initiatives, such as mining or cash-crops, meant that land historically used for food gathering became inaccessible or infertile, the team concluded.

And pollution from colonial shipping lines and industry degraded reefs, a former rich food source.

Professor Stanley Ulijaszek said: “Previous attempts to explain the disproportionately high rates of obesity in these and other island nations have tended to focus on the geographical isolation of islands and the risk of food shortages.

“Theories have suggested that islanders are genetically predisposed to putting on weight, but we believe this does not explain why obesity has emerged so rapidly on these islands.

“Interventions that tap into the naturally occurring social networks on the islands provide a new, and we believe more effective, way of tackling obesity.”

The team scoured existing academic literature and archive documents about the islands from libraries in Australia, Nauru and the UK.

They also interviewed people on the islands and lived there themselves for a short time to observe daily life first-hand.